Time-extended cooling system for line-powered apparatus

ABSTRACT

Certain electrical systems, such as projectors, contain components, which get very hot and require active cooling systems. During normal operation, a switch operates a cooling fan from a primary power supply. Upon detecting a failure in the primary power supply, the switch connects the cooling fan to a secondary power supply.

FIELD OF THE INVENTION

The present invention relates generally to cooling systems, and more particularly to line-powered electrical devices that generate heat.

BACKGROUND OF THE INVENTION

Many electrical devices and systems require active cooling systems to prevent over-heating. In passive cooling systems, the heat generated from internal components is conducted away to a cooler area via a path of sufficiently low thermal resistance. If the thermal resistance is too high or if the temperature difference is too small to support sufficient heat flow, active cooling systems must be employed. Forced air-cooling is often used for this purpose. It effectively lowers the thermal resistance, and thus lowers the temperature rise with respect to ambient conditions for a given amount of thermal energy.

In some systems, the heat generating components can get extremely hot. The temperature inside the component is often sufficient to destroy neighboring parts, unless the components are cooled. For example, the temperature inside a video projector bulb can exceed several thousand degrees. Damage is prevented by keeping the thermal resistance from those surrounding areas to the ambient air as low as possible compared to the thermal resistance from the heat source to the surrounding areas. In effect, the very high temperatures are contained in a small area through this thermal resistance mismatch. Often, a fan or other cooling device is employed to keep the outer thermal resistance as low as possible.

It is useful to consider what happens when line-power is suddenly lost in actively cooled equipment with a high temperature component. Although no further heat is generated in the component, the thermal mass of the component has stored some amount of heat energy, which must be dissipated. Thus, heat continues to flow out of the component. If an active cooling system ceases to function, the outer thermal resistance increases, slowing the flow of heat to the ambient environment, and in effect, creating an outer, somewhat more thermally insulated layer. This can cause a dramatic temperature rise in the parts surrounding the hot component, which can be destructive.

To combat this problem, many electronic systems with hot components have a special power-down cycle, which immediately removes power from the heat-generating component, but continues to run the cooling system for sufficient time to cool down the hot component. A severe problem arises if all power is lost unexpectedly, and a normal cool down cycle is not possible. For video projectors, sudden loss of power and the resulting inability to properly cool the lamp results in a premature device failure. There is a clear need for a method of cooling devices and systems in a controlled manner, even in the event of the loss of line power.

A similar thermal problem occurs in an internal combustion engine, where heat must be dissipated after the engine has been turned off. U.S. Pat. No. 5,828,967 describes a method of using a by-pass line to continue to run the cooling fan for some time after the engine is turned off. In this case, the fan power comes typically from a battery. Because the battery is needed to start the engine, the amount of energy that is used for running the fan after shutdown is minimized.

U.S. Pat. No. 6,472,828 describes a method for controlling fan speed in a projector in order to allow faster bulb turn-on. By running the fan at low speeds initially, the thermal resistance is momentarily higher, allowing the temperature to rise rapidly. The fan speed is then increased to prevent overheating during normal operation. However, the system does not address cool down in the event of line power loss.

U.S. Pat. No. 5,938,407 addresses an entirely different problem. There, it is desired to keep a coal stove fire as hot as possible in the event of a primary power loss. That system includes two motors that run a fan. The backup motor mechanically engages with the fan, and an alternate power source controlled by a backup circuit. When power is lost, a solenoid is de-energized, depressing a switch and completing the backup circuit to the alternate power source. The backup motor rotates into contact with the fan to ensure uninterrupted airflow. That backup system is for powering an air distribution fan that ensures sufficient oxygen reaches a coal fire burning within a coal stove to maintain the coal fire hot until primary power is restored.

Many clocks have a battery-backup feature. In this case, time keeping is the issue rather than thermal concerns. Similarly, backup generators and uninterruptible power supplies are commonly used to keep computers and other vital equipment running during a power failure.

Various thermal fuses and other protection devices exist which cut power to equipment when excessive temperatures are detected. They do not function in the event of a power failure.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide cooling to high temperature components in electronic equipment in the event of the loss of line power.

It is another objective of the invention to prevent damage to electrical equipment in the event of the loss of line power as caused by the stored heat of certain high temperature components.

The electrical equipment containing the invention is provided with an energy storage device. This energy storage device receives and stores energy during normal line-powered operation. When line power is lost, the energy storage device provides power to operate an active cooling system for a period of time sufficient to prevent thermal damage.

The energy storage device can take one or more forms, including, but not limited to the following: a battery, a capacitor, a spring, a flywheel, a compressed gas, and the like.

The cooling system can take one or more of a plurality of forms, including, but not limited to the following: a fan, a liquid cooling system, a Peltier device, a refrigeration system, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system using a time-extended cooling apparatus according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a projector system 100 that uses the invention. It should be understood that the invention can also be used by other heat generating electrical systems and devices.

The projector includes a heat source 110, i.e., a lamp. The temperature of the lamp can reach several thousand degrees. If the lamp gets too hot, then it can self-destruct, as well as damage nearby components. Therefore, during normal operation, a fan 120 is used to cool the lamp. The fan is connected to a primary power supply 130, normally a power line.

In most modern projectors, the fan will continue to run for several minutes after the projector has been shut off to cool the lamp. However, should there be a failure in the power line, damage can still occur.

Therefore, the projector 100 also includes a secondary power supply 140, for example, a rechargeable battery. Should there be a failure in the primary power supply, then a switch 150 can cause the fan 120 to be operated from the secondary power supply until a sensor 160 determines that the lamp has cooled sufficiently. The sensor can also control the speed of the fan to maximize battery lifetime.

In the preferred embodiment, the rechargeable battery is contained in an accessible compartment 170. The switch or another simple sensor determines the presence or absence of the battery. If the battery is not installed, or the battery is low in charge, an audible or visual warning can be given. Alternatively, a network can be used to send an alert message to a system operator.

An alternative embodiment of the invention embeds the secondary power supply, sensor and switch in the fan. A fan thus configured can be installed in any place where time-extended cooling is required.

It is possible to use mechanical energy storage devices to the same effect. In another alternative embodiment, the fan is modified to wind a clock spring to a certain tension and maintain it at a given level. When primary power is removed, the spring provides the power to spin the fan for some additional time.

Although the invention has been described by way of examples of preferred embodiments, it is to be understood that various other adaptations and modifications may be made within the spirit and scope of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications. 

1. A time-extended cooling apparatus, comprising: means for cooling; a primary power supply connected to the means for cooling; a secondary power supply connected to the means for cooling; means for operating the means for cooling from the primary power supply; means for sensing a failure in the primary power supply; and means for switching the means for cooling to the secondary power supply in response to sensing the failure in the primary power supply.
 2. The apparatus of claim 1 wherein the means for cooling is a fan.
 3. The apparatus of claim 1 wherein the means for cooling is a liquid cooling system.
 4. The apparatus of claim 1 wherein the means for cooling is a Peltier device.
 5. The apparatus of claim 1 wherein the means for cooling is a refrigeration system.
 6. The apparatus of claim 1 further comprising: a projector lamp generating heat.
 7. The apparatus of claim 1 wherein the secondary power supply is a rechargeable battery.
 8. The apparatus of claim 1 wherein the secondary power supply, means for operating, means for sensing, and means for switching are embedded in the means for cooling.
 9. The apparatus of claim 1 wherein the secondary power supply is a spring.
 10. The apparatus of claim 1 wherein the secondary power supply is a capacitor.
 11. The apparatus of claim 1 wherein the means for operating maximizes a time the means for cooling operates.
 12. The apparatus of claim 1 further comprising: means for sensing a temperature of a component cooled by the means for cooling.
 13. The apparatus of claim 1 further comprising: a heat sensitive device; means for sensing a temperature of the heat sensitive device; and means for operating the means for cooling from the secondary power supply until the heat sensitive device reaches a predetermine reduced temperature.
 14. The apparatus of claim 13 wherein the heat sensitive device is a projector lamp.
 15. A time-extended cooling apparatus, comprising: means for cooling mounted in close proximity to a lamp in a projector; a primary power supply connected to the means for cooling; a secondary power supply connected to the means for cooling; means for operating the means for cooling from the primary power supply; means for sensing a failure in the primary power supply; means for sensing a temperature of the lamp; and means for switching the means for cooling to the secondary power supply in response to sensing the failure in the primary power supply until the lamp reaches a predetermined reduced temperature.
 16. A method for time-extended cooling, comprising: operating a cooling system from a primary power supply; sensing a failure in the primary power supply; and operating the cooling system from a secondary power supply in response to sensing the failure in the primary power supply.
 17. The method of claim 15 further comprising: sensing a temperature of a heat sensitive device; and operating the cooling system from a secondary power supply until the heat sensitive device reaches a predetermined reduced temperature. 